The evolution of cooperative breeding; is there cheating?

Over the past four decades biologists have developed a body of theory to explain the evolution of cooperative behavior. Three key conditions have been modeled in which the fitness of individuals can be enhanced by their cooperative acts. Cooperation can evolve and be stable when (i) cooperative individuals share genes with the recipients (Hamilton, 1964a,b), (ii) when cooperation is a byproduct of selfish action (West-Eberhard, 1975; Brown, 1983; Connor, 1986), and (iii) when there is directed reciprocation for cooperative acts (Trivers, 1971; Axelrod and Hamilton, 1981; Sachs et al., 2004). Cooperative breeding is a common example of cooperation observed in numerous species of vertebrates and invertebrates; it occurs when some members of a social group delay independent breeding and help others raise young (Brown, 1987). In their struggle to understand why individuals should invest in the offspring of others, biologists have developed an exclusive, and sometimes idiosyncratic, set of models to explain the evolutionary maintenance of cooperative breeding (e.g. Gaston, 1978; Woolfenden and Fitzpatrick, 1978; Wiley and Rabenold, 1984; Jamieson, 1989; Emlen et al., 1991; Connor and Curry, 1995; Zahavi, 1995; Cockburn, 1998; Clutton-Brock, 2002; Kokko et al., 2001, 2002). Despite the wealth of theory to explain the evolution of cooperative breeding, it is not immediately evident how these hypotheses relate to one another or to general theories of cooperation (Axelrod and Hamilton, 1981; Queller, 1985; Bull and Rice, 1991; Connor, 1995; Sachs et al., 2004; Foster and Wenseleers, 2006; Lehmann and Keller, 2006). Bergmüller et al. (2007) attempted to bridge the theoretical divide between the evolution of cooperation and cooperative breeding. They developed a seven part classification system for cooperation theory and used it to connect hypotheses for the maintenance of cooperative breeding in vertebrates. Here, we review a simpler, tripartite framework for the evolution of